ECE6604

PERSONAL & MOBILE COMMUNICATIONS

GORDON L. STÜBER

School of Electrical and Computer EngineeringGeorgia Institute of TechnologyAtlanta, Georgia, 30332-0250

Ph: (404) 894-2923Fax: (404) 894-7883

E-mail: stuber@ece.gatech.eduURL: http://www.ece.gatech.edu/users/stuber/6604

1

TOPICAL OUTLINE

1. INTRODUCTION TO CELLULAR RADIO SYSTEMS

2. MULTIPATH-FADING CHANNEL MODELLING AND SIMULATION

3. SHADOWING AND PATH LOSS

4. CO-CHANNEL INTERFERENCE AND OUTAGE

5. SINGLE- AND MULTI-CARRIER MODULATION TECHNIQUESAND THEIR POWER SPECTRUM

6. DIGITAL SIGNALING ON FLAT FADING CHANNELS

7. MULTI-ANTENNA TECHNIQUES

8. ADVANCED TOPICS

• MULTICARRIER TECHNIQUES• SPREAD SPECTRUM TECHNIQUES• CELLULAR ARCHITECTURES AND RESOURCE MANAGE-

MENT

2

ECE6604

PERSONAL & MOBILE COMMUNICATIONS

Week 1

Introduction,

Path Loss, Co-channel Interference, Link Budget

3

WIRELESS INFRASTRUCTURE

1. Satellite Networks

2. Broadcast Networks

3. Cellular Telephony Systems

4. Paging Networks

5. Fixed Wireless Access Systems

6. Wireless Local Area Networks

7. Personal Area Networks

8. Sensor Networks

4

Overview 3GPP2 C.S0024 Ver 4.0

Air LinkManagement

Protocol

OverheadMessagesProtocol

PacketConsolidation

Protocol

InitializationState Protocol

Idle StateProtocol

ConnectedState Protocol

Route UpdateProtocol

SessionManagement

Protocol

SessionConfiguration

Protocol

StreamProtocol

SignalingLink

Protocol

Radio LinkProtocol

SignalingNetworkProtocol

ControlChannel MAC

Protocol

Access ChannelMAC Protocol

Reverse TrafficChannel MAC

Protocol

Forward TrafficChannel MAC

Protocol

ConnectionLayer

SessionLayer

StreamLayer

ApplicationLayer

MACLayer

SecurityLayer

PhysicalLayer

SecurityProtocol

AuthenticationProtocol

EncryptionProtocol

Default PacketApplication

Default SignalingApplication

LocationUpdateProtocol

AddressManagement

Protocol

KeyExchangeProtocol

Physical LayerProtocol

FlowControlProtocol

1

Figure 1.6.6-1. Default Protocols 2

3

5

P r o d u c t B r i e f

A p p l i c a t i o n E x a m p l e Q u a d - B a n d E G P R S S o l u t i o n

Power BusPeripherals

I2CInterface

Power BusBaseband

I2C

AC-Adaptor

Charger

Pre-Charge

VBB2

VRTC

VBB1

VMemory

VBB USB

VBB Analog

VBB I/O Hi

VUSB Host

SM-POWER(PMB 6811)

Control

BB (LR)/Mem/CoproStep down 600 mA

On-chipReference

VBT BB

VRF3 (BT)

VRF Main

VRF VCXO

AmpVDD

LEDDriver

MotorDriver

M

NiMH/LiIonBattery

Power BusBluetooth

Power BusRF

S-GOLD2(PMB 8876)

DA

A

AD

D

I2S / DAII2S SSC

TEAKLite®

GPTU IR-Memory

GSMCipher Unit

RFControl

Speechand Channel

DecodingEqualizer

DA

AD

Speechand Channel

Encoding

8 PSK/GMSKModulator

DA

AD

SRAM

MOVE Copro

DMAC ICUKeypad

USB FSOTG

FastIrDA

MMC/SDIF

CAPCOM

GPTU

RTC

I2C

JTAG

AUXADC

SCCU

FCDP

EBU

GSMTimer

GEA-1/2/3 CGUAFC

GPIOs

ARM®926 EJ-SUSIM

USARTsSSCUSIF CameraIFDisplay

IF

Multimedia IC IF

FLASH/SDRAM

SMARTi DC+(PMB 6258) GSM 900/1800

GSM 850/1900

AtomaticOffset

Compensation

ControlLogic

SAMFast PLL

850

900

1800

1900

Rx/Tx

Multi ModePA

850900

18001900

I

QCLKDATENA

AFC

RF Control

26 MHz

Car Kit

Earpiece

Ringer

Headset

MUX

0* #

321

8

54

7

SDCMMC

6

9

6

1G Cellular Technologies

• 1979 — Nippon Telephone and Telegraph (NTT) introduces thefirst cellular system in Japan.

• 1981 — Nordic Mobile Telephone (NMT) 900 system introduced byEricsson Radio Systems AB and deployed in Scandinavia.

• 1984 — Advanced Mobile Telephone Service (AMPS) introducedby AT&T in North America.

Feature NTT NMT AMPSFrequency Band 925-940/870-885 890-915 824-849RL/FLa 915-918.5/860-863.5 917-950 869-894(MHz) 922-925/867-870Carrier Spacing 25/6.25 12.5b 30(kHz) 6.25

6.25Number of 600/2400 1999 832Channels 560

280Modulation analog FM analog FM analog FMaRL = reverse link, FL = forward linkb frequency interleaving using overlapping channels, where the channelspacing is half the nominal channel bandwidth.

7

2G Cellular Technologies

• 1990 — Interim Standard IS-54 (USDC) adopted by TIA.

• 1991 — Japanese Ministry of Posts and Telecommunications stan-dardized Personal Digital Cellular (PDC)

• 1992 — Phase I GSM system is operational (September 1).

• 1993 — Interim Standard IS-95A (CDMA) adopted by TIA.

• 1994 — Interim Standard IS-136 adopted by TIA.

• 1998 — IS-95B standard is approved.

• 2011 — GSM is deployed in 219 countries, 5.2B subscribers, covers80% of world population. IS-95A/B is deployed in 121 countries,IS-54/136 is extinct, PDC is nearly extinct.

8

2G Cellular Technologies

Feature GSM/DCS1800/PCS1900 IS-54/136Frequency Band GSM: 890-915/ 824-829/RL/FLa 935-960 869/894(MHz) DCS1800: 1710-1785/ 1930-1990/

1805-1880 1850-1910PCS1900: 1930-1990/1850-1910

Multiple Access F/TDMA F/TDMACarrier Spacing (kHz) 200 30Modulation GMSK π/4-DQPSKBaud Rate (kb/s) 270.833 48.6Frame Size (ms) 4.615 40Slots/Frame 8/16 3/6Voice Coding (kb/s) VSELP(HR 6.5) VSELP (FR 7.95)

RPE-LTP (FR 13) ACELP (EFR 7.4)ACELP (EFR 12.2) ACELP (12.2)

Channel Coding Rate-1/2 CC rate-1/2 CCFrequency Hopping yes noHandoff hard hard

9

2G Cellular Technologies

Feature PDC IS-95Frequency Band 810-826/ 824-829/RL/FLa 940-956 869-894(MHz) 1429-1453/ 1930-1990/

1477-1501 1850-1910Multiple Access F/TDMA F/CDMACarrier Spacing (kHz) 25 1250Modulation π/4-DQPSK QPSKBaud Rate (kb/s) 42 1228.8 Mchips/sFrame Size (ms) 20 20Slots/Frame 3/6 1Voice Coding (kb/s) PSI-CELP (HR 3.45) QCELP (8,4,2,1)

VSELP (FR 6.7) RCELP (EVRC)Channel Coding rate-1/2 BCH FL: rate-1/2 CC

RL: rate-1/3 CCFrequency Hopping no N/AHandoff hard soft

10

3G Cellular Technologies

• 1998 — A group called 3GPP (Third Generation Partnership Project)is created to] produce a common 3G standard based on WCDMA.

• 1999 — The group 3GPP2 is created to harmonize the use of multi-carrier cdma2000

• 2000 — South-Korean Telecom (SKT) launches cdma2000-1X net-work (DL/UL: 153 kbps)

• 2001 — NTT DoCoMo deploys commercial UMTS network in Japan

• 2002 — cdma2000 1xEV-DO (UL: 153 kbps, DL: 2.4 Mb/s)

• 2003 — WCDMA (UL/DL: 384 kbps)

• 2006 — HSDPA (UL: 384 kbps, DL: 7.2 Mbps)

• 2007 — cdma2000 1xEV-DO Rev A (UL: 1.8 Mbps, DL: 3.1 Mbps)

• 2010 — HSDPA/HSUPA (UL: 5.8 Mbps, DL: 14.0 Mbps), cdma20001xEV-DO Rev A (UL: 1.8 Mbps, DL: 3.1 Mbps)

11

• 2011 — 1 in 4 HSPA networks have HSPA+ (UL: 11 Mbps, DL:42 Mbps), LTE is currently deployed by 16 carriers with 57 moredeployments committed

• future — LTE-A (UL: 50 Mbps, DL: 100 Mbps), cdma2000 1xEV-DO Rev B (UL: 5.4 Mbps, DL: 14.7 Mbps)

3G Cellular Technologies

Feature W-CDMA cdma2000Multiple Access DS-CDMA DS-CDMAChip Rate (Mcps) 3.84 1.2288Carrier Spacing (MHz) 5 1.25Frame Length (ms) 10 5/20Modulation FL: QPSK FL: BPSK/QPSK

RL: BPSK RL: BPSK64-ary orthogonal

Coding rate-1/2, 1/3 rate-1/2, 1/3, 1/4,K = 9 conv. code 1/6 K = 9 conv. coderate-1/3 rate-1/2, 1/3, 1/4,K = 4 turbo code 1/5, K = 4 turbo code

Interleaving inter/intraframe intraframeSpreading FL: BPSK complex

RL: QPSKInter BS asynchronous synchronoussynchronization

12

3G & 4G Cellular Technologies

• Cellular operators are heavily invested in 3G infrastructures.– 1Q 2011: 5.2B GSM and 577 cdmaOne subscribers; 575M

CDMA2000 and 717M WCDMA subscribers

• LTE: Currently seeing some deployment (700 MHz band in NorthAmerica), sometimes branded as 4G but does not meet 4G require-ments.

– Develop LTE-A (4G) in parallel with evolved 3G.

• Evolved HSPA (HSPA+) is evolutionary– Can achieve the data rates as LTE-A in 5 MHz with HSPA+

∗ Receiver diversity∗ Equalization and Interference cancellation∗ MIMO (2 x 2)∗ High-order signal constellations (64 QAM)

– In August 2009 there were 12 HSPA+ networks in the worldrunning at 21 Mbps (DL). Today 1 out of 4 HSPA networkshave HSPA+ in commercial operation.

13

WIRELESS LANs (WiFi)

• IEEE 802.11 – Direct Sequence Spread Spectrum (1-and-2 Mb/s,2.4GHz)

• IEEE 802.11b – Complimentary Code Keying (CCK) (5.5-and-11Mb/s, 2.4GHz)

• IEEE 802.11g/a – Orthogonal Frequency Division Multiplexing (OFDM)(6-to-54 Mb/s, 2.4/5GHz)

• IEEE 802.11e – MAC enhancements for Quality of Service (QoS)

• IEEE 802.11i – Security

• IEEE 802.11n – MIMO physical layer

• Femtocells: integrate WiFi with cellular.– Benefit: Frees up cellular capacity and reduces BS power con-

sumption.

– Drawback: MS power drain due to WLAN searching.

– Drawback Fast WLAN-to-cellular handoff is needed to preventdropped calls.

14

WIRELESS PANs

• IEEE Std 802.15.1-2002 - 1Mb/s WPAN/Bluetooth v1.x derivativework - uses frequency hop spread spectrum.

– Today Bluetooth is managed by the Bluetooth Special InterestGroup.

• P802.15.2- Recommended Practice for Coexistence in UnlicensedBands

• P802.15.3 - 20+ Mb/s High Rate WPAN for Multimedia and DigitalImaging

• P802.15.3a - 110+ Mb/s Higher Rate Alternative PHY for 802.15.3- Ultra wideband (UWB)

• P802.15.4 - 200 kb/s max for interactive toys, sensor and automa-tion needs

• Applications include (mobile) ad hoc networks, sensor networks

15

WIRELESS MANs (WiMax)

• IEEE 802.16 addresses the ”first-mile/last-mile” connection in wire-less MANs.

– focuses on the efficient use of bandwidth between 10 and 66 GHz(the 2 to 11 GHz region with PMP and optional Mesh topologies)

– defines a medium access control (MAC) layer that supports mul-tiple physical layer specifications customized for the frequencyband of use.

• IEEE 802.16e - mobility extension of IEEE802.16.

• IEEE802.16-2009 had a relatively slow start - 250 trials and networkstoday.

– 17.25M subscribers worldwide in 1Q 2011; 400K WiMax and50M 3G subscribers added in 1Q 2009.

– Competing solutions:

∗ Digital Subscriber Line (DSL), Coax Cable Networks∗ Satellite DSL∗ 3G cellular with HSPA+ or cdma2000 1X EV-DO Rev A

16

FREQUENCY RE-USE AND THE CELLULAR

CONCEPT

CD

B

A

4-Cell

C

AB

3-Cell 7-Cell

A

C

F

D

GE

B

Commonly used hexagonal cellular reuse clusters.

• Tessellating hexagonal cluster sizes, N, satisfyN = i2 + ij + j2

where i, j are non-negative integers and i ≥ j.– hence N = 1, 3, 4, 7, 9, 12, . . .

17

B

G

F

G

D

B

C

G

A

F

B

G

D

E

C

A

E

C

A

F

B

A

F

G

D

D

E

C

A

F

G

B

Cellular layout using seven-cell reuse clusters.

• Real cells are not hexagonal.

• Frequency reuse introduces co-channel interference and adjacentchannel interference.

18

CO-CHANNEL REUSE FACTOR

A

AD

R

Frequency reuse distance for 7-cell clusters.

• For hexagonal cells, the co-channel reuse factor isD

R=

√3N

19

RADIO PROPAGATION MECHANISMS

• Radio propagation is by three mechanisms– Reflections off objects larger than a wavelength

– Diffraction around the edges of objects

– Scattering by objects smaller than a wavelength

• A mobile radio environment is characterized by three nearly inde-pendent propagation factors

– Path loss attenuation with distance.

– Shadowing caused by large obstructions such as buildings, hillsand valleys.

– Multipath-fading caused by the combination of multipath propa-gation and transmitter and/or receiver movement.

20

FREE SPACE PATH LOSS (FSPL)

• Equation for free-space path loss is

LFS =

(4πd

λc

)2.

and encapsulates two effects.

1. The first effect says that spreading out of electromagnetic energyin free space is determined by the inverse square law, i.e.

Ωr(d) = Ωt1

4πd2,

where

– Ωt is the total transmit power

– Ωr(d) is the received power per unit area or power spatial den-sity (in watts per meter-squared) at distance d. Note that thisterm is not frequency dependent.

21

FREE SPACE PATH LOSS (FSPL)

• Second effect2. The second effect is due to aperture, which determines how well

an antenna picks up power from an incoming electromagneticwave. For an isotropic antenna, we have

Ωp(d) = Ωr(d)λ2c4π

,

where Ωp(d) is the received power. Note that this is entirely de-pendent on wavelength, λc, which is how the frequency-dependentbehavior arises.

• For free space propagation the path loss is

LFS (dB) =Ωt

Ωp(d)= 10log10

{(4πd

λc

)2}

= 10log10

{(4πd

c/fc

)2}

= 20log10fc +20log10d− 147.55 dB .

22

PROPAGATION OVER A FLAT SPECULAR SURFACE

d1

d2

BS

MS

d

hbhm

1

• The length of the direct path is

d1 =√

d2 + (hb − hm)2

and the length of the reflected path is

d2 =√

d2 + (hb + hm)2

d = distance between mobile and base stationshb = base station antenna heighthm = mobile station antenna height

• Given that d � hbhm, we have d1 ≈ d and d2 ≈ d.

• However, since the wavelength is small, the direct and reflectedpaths may add constructively or destructively over small distances.The carrier phase difference between the direct and reflected pathsis

φ2 − φ1 = 2πλc

(d2 − d1)

2

• Taking into account the phase difference, the received signal poweris

μΩp = Ωt

(λc

4πd

)2 ∣∣∣1+ ae−jbej(φ2−φ1)∣∣∣2 ,where a and b are the amplitude attenuation and phase change in-troduced by the flat reflecting surface.

• If we assume a perfect specular reflection, then a = 1 and b = π forsmall θ. Then

μΩp = Ωt

(λc

4πd

)2 ∣∣∣1− ej(2πλcΔd)∣∣∣2= Ωt

(λc

4πd

)2 ∣∣∣∣1− cos(2π

λcΔd

)− j sin

(2π

λcΔd

)∣∣∣∣2

= Ωt

(λc

4πd

)2 [2− 2cos

(2π

λcΔd

)]

= 4Ωt

(λc

4πd

)2sin2

(π

λcΔd)

)where Δd = (d2 − d1).

3

• Given that d � hb and d � hm, and applying the approximation√1+ x ≈ 1+ x/2 for small x, we have

Δd ≈ d(1+

(hb + hm)2

2d2

)− d

(1+

(hb − hm)22d2

)=

2hbhmd

.

• Finally, the received envelope power is

μΩp ≈ 4Ωt(

λc

4πd

)2sin2

(2πhbhm

λcd

)

• Under the condition that d � hbhm, the above reduces to

μΩp ≈ Ωt(hbhm

d2

)2where we have invoked the small angle approximation sin x ≈ x forsmall x.

• Propagation over a flat specular surface differs from free space prop-agation in two respects

– it is not frequency dependent

– signal strength decays with the with the fourth power of thedistance, rather than the square of the distance.

4

10 100 1000 10000Path Length, d (m)

10

100

1000

Path

Los

s (d

B)

Propagation path loss Lp (dB) with distance over a flat reflecting surface;hb = 7.5 m, hm = 1.5 m, fc = 1800 MHz.

LFL =

[(λc

4πd

)24 sin2

(2πhbhm

λcd

)]−1

5

• In reality, the earth’s surface is curved and rough, and the signalstrength typically decays with the inverse β power of the distance,and the received power at distance d is

μΩp(d) =μΩp(do)

(d/do)β

where μΩp(do) is the received power at a reference distance do.

• Expressed in units of dBm, the received power isμΩp (dBm)(d) = μΩp (dBm)(do)− 10β log10(d/do) (dBm)

• β is called the path loss exponent. Typical values of μΩp (dBm)(do) andβ are have been determined by empirical measurements for a varietyof areas

Terrain μΩp (dBm)(do = 1.6 km) β

Free Space -45 2Open Area -49 4.35North American Suburban -61.7 3.84North American Urban (Philadelphia) -70 3.68North American Urban (Newark) -64 4.31Japanese Urban (Tokyo) -84 3.05

6

Co-channel Interference

Worst case co-channel interference on the forward channel.

7

Worst Case Co-Channel Interference

• For N = 7, there are six first-tier co-channel BSs, located at dis-tances {√13R,4R,√19R,5R,√28R,√31R} from the MS.

• Assuming that the BS antennas are all the same height and all BSstransmit with the same power, the worst case carrier-to-interferenceratio, Λ, is

Λ =R−β

(√13R)−β + (4R)−β + (

√19R)−β + (5R)−β + (

√28R)−β + (

√31R)−β

=1

(√13)−β + (4)−β + (

√19)−β + (5)−β + (

√28)−β + (

√31)−β

.

• With a path loss exponent β = 3.5, the worst case Λ is

Λ(dB) =

⎧⎨⎩

14.56 dB for N = 79.98 dB for N = 47.33 dB for N = 3

.

– Shadows will introduce variations in the worst case Λ.

8

Cell Sectoring

Worst case co-channel interference on the forward channel with 120o cellsectoring.

9

• 120o cell sectoring reduces the number of co-channel base stationsfrom six to two. For N = 7, the two first tier interferers are locatedat distances

√19R,

√28R from the MS.

• The carrier-to-interference ratio becomes

Λ =R−β

(√19R)−β + (

√28R)−β

=1

(√19)−β + (

√28)−β

.

• Hence

Λ(dB) =

⎧⎨⎩

20.60 dB for N = 717.69 dB for N = 413.52 dB for N = 3

.

• For N = 7, 120o cell sectoring yields a 6.04 dB C/I improvementover omni-cells.

• The minimum allowable cluster size is determined by the thresholdΛ, Λth, of the radio receiver. For example, if the radio receiver hasΛth = 15.0 dB, then a 4/12 reuse cluster can be used (4/12 means4 cells or 12 sectors per cluster).

10

Receiver Sensitivity

• Receiver sensitivity refers to the ability of the receiver to detectradio signals. We would like our radio receivers to be as sensitive aspossible.

• Radio receivers must detect radio waves in the presence of noiseand interference.

– External noise sources include atmospheric noise (e.g, lightningstrikes), galactic noise, man made noise (e.g, automobile ignitionnoise), co-channel and adjacent channel interference.

– Internal noise sources include thermal noise.

• The ratio of the desired signal power to thermal noise power beforedetection is commonly called the carrier-to-noise ratio, Γ.

• The parameter Γ is a function of the communication link parametersincluding transmitted power (or effective isotropic radiated power(EIRP)), path loss, receiver antenna gain, and the effective input-noise temperature of the receiving system.

• The formula that relates the link parameters to Γ is called the linkbudget.

11

Link Budget

• The link budget can be expressed in terms of the following param-eters:

Ωt = transmitted carrier powerGT = transmitter antenna gainLp = path lossGR = receiver antenna gainΩp = received signal powerEs = received energy per modulated symbolTo = receiving system noise temperature in degrees KelvinBw = receiver noise equivalent bandwidthNo = white noise power spectral densityRc = modulated symbol ratek = 1.38× 10−23 = Boltzmann’s constantF = noise figure, typically about 3 dB

LRX = receiver implementation lossesLI = losses due to system load (interference)

Mshad = shadow marginGHO = handoff gainΩth = receiver sensitivity

12

Noise Equivalent Bandwidth, Bw

• Consider an arbitrary filter with transfer function H(f).

• If the input to the filter is a white noise process with power spectraldensity No/2 watts/Hz, then the noise power at the output of thefilter is

Nout =No

2

∫ ∞−∞

|H(f)|2df

= No

∫ ∞0

|H(f)|2df

• Next suppose that the same white noise process is applied to anideal low-pass filter with bandwidth Bw and d.c. response H(0). Thenoise at the output of the filter is

Nout = NoBwH2(0)

• Equating the above two equations give the noise equivalent bandwdith

Bw =

∫∞0 |H(f)|2df

H2(0)

13

• The effective received carrier power is

Ωp =ΩtGTGRLRXLp

.

• The total input noise power to the detector isN = kToBwF

• Very often the following kTo value at room temperature of 17 oC(290 oK) is used kTo = −174 dBm/Hz,

• The received carrier-to-noise ratio defines the link budget

Γ =ΩpN

=ΩtGTGR

kToBwFLRXLp.

• The carrier-to-noise ratio, Γ, and modulated symbol energy-to-noiseratio, Es/No, are related as follows

Es

No= Γ× Bw

Rc.

• Hence, we can rewrite the link budget asEs

No=

ΩtGTGRkToRcFLRXLp

.

14

• Converting into decibel units givesEs/No(dB) = Ωt (dBm) +GT (dB) +GR (dB) (1)

−kTo(dBm)/Hz −Rc (dB Hz) − F(dB) − LRX (dB) − Lp (dB) .

• The receiver sensitivity is defined asΩth = LRXkToF (Es/No)Rc

or converting to decibel units

Ωth (dBm) = LRX (dB) + kTo(dBm/Hz) + F(dB) + Es/No(dB) +Rc (dB Hz) .

• All parameters are usually fixed except for Es/No. The receiver sen-sitivity (in dBm) is determined by the minimum acceptable Es/No.

• Substituting the determined receiver sensitivity Ωth (dBm) into (1) andsolving for Lp (dB) gives the maximum allowable path loss

Lmax (dB) = Ωt (dBm) +GT (dB) +GR (dB) −Ωth (dBm) .

15